Peak Transmission Efficiency Research Articles

Pixelated Filter Array for On-Chip Polarized Spectral Detection.

On-chip multi-dimensional detection systems integrating pixelated polarization and spectral filter arrays are the latest trend in optical detection instruments, showing broad application potential for diagnostic medical imaging and remote sensing. However, thin-film or microstructure-based filter arrays typically have a trade-off between the detection dimension, optical efficiency, and spectral resolution. Here, we demonstrate novel on-chip integrated polarization spectral detection filter arrays consisting of metasurfaces and multilayer films. The metasurfaces with two nanopillars in one supercell are designed to modulate the Jones matrix for polarization selection. The angle of diffraction of the metasurfaces and the optical Fabry-Perot (FP) cavities determine the spectrum's center wavelength. The polarization spectral filter arrays are placed on top of the CMOS sensor; each array corresponds to one pixel, resulting in high spectral resolution and optical efficiency in the selected polarization state. To verify the methodology, we designed nine-channel polarized spectral filter arrays in a wavelength range of 1350 nm to 1550 nm for transverse electric (TE) linear polarization. The array has a 10 nm balanced spectral resolution and average peak transmission efficiency of over 75%, which is maintained by utilizing lossless dielectric material. The proposed array can be fabricated using overlay e-beam lithography, and the process is CMOS-compatible. The proposed array enables broader applications of in situ on-chip polarization spectral detection with high efficiency and spectral resolution, as well as in vivo imaging systems.

Integrated nanophotonic optical diodes designed by genetic algorithms.

Integrable nanophotodiode devices have attracted much research interest in recent years because of their potential applications in all-optical computing and optical communication systems. We propose a new optical diode design scheme. We use genetic algorithms (GAs) to design an optical diode, which has a device footprint of only 2.5×2.5µm2. These devices designed by GA have the ability to achieve high-efficiency unidirectional transmission. Simulations show the forward transmission efficiency can reach higher than 65% for a Gaussian beam between the wavelengths of 1400 and 1600 nm, and the peak transmission efficiency reaches 75%. The transmission contrast at the design wavelength between 1500 and 1600 nm is higher than 90%, which meets the requirements of high unidirectionality, wide operational bandwidth, and small scale. The devices have more advantages for optical diodes compared with structures designed by photonic crystals and gratings. The application of this scheme provides a new idea for the design and research of all-optical diodes in the field of optical communication.

Ultra-compact primary colors filter based on plasmonic digital metamaterials

A novel primary colors filter (RGB filter) is designed with ultra-compact size by using the inverse design method. The core size of filter goes to 0.5μm×0.55μm, and then the chip integration being high enhanced. The transmission characteristics of RGB filtering are simulated by FDTD algorithm. A high performance and high compact coupling region can be obtained by using inverse design method to search a full-parameter space. In addition, we investigate the relationship between the filtering performance and the digital unit size, and prove the good performance tolerance with different digital unit size. The average peak transmission efficiencies are over 70% and the average channel crosstalk are about −16 dB at 450 nm, 550 nm and 650 nm, for each channel, respectively. High performance is achieved for this RGB filter with a footprint of only 0.5μm×0.55μm, and is suitable for optical device integration.

Ultralow-light-level color image reconstruction using high-efficiency plasmonic metasurface mosaic filters

As single-photon imaging becomes progressively more commonplace in sensing applications such as low-light-level imaging, three-dimensional profiling, and fluorescence imaging, there exist a number of fields where multispectral information can also be exploited, e.g., in environmental monitoring and target identification. We have fabricated a high-transmittance mosaic filter array, where each optical filter was composed of a plasmonic metasurface fabricated in a single lithographic step. This plasmonic metasurface design utilized an array of elliptical and circular nanoholes, which produced enhanced optical coupling between multiple plasmonic interactions. The resulting metasurfaces produced narrow bandpass filters for blue, green, and red light with peak transmission efficiencies of 79%, 75%, and 68%, respectively. After the three metasurface filter designs were arranged in a 64 × 64 format random mosaic pattern, this mosaic filter was directly integrated onto a CMOS single-photon avalanche diode detector array. Color images were then reconstructed at light levels as low as approximately 5 photons per pixel, on average, via the simultaneous acquisition of low-photon multispectral data using both three-color active laser illumination and a broadband white-light illumination source.

Inverse designed tunable four-channel wavelength demultiplexer

Traditional wavelength demultiplexers are usually designed by brute-force parameter sweeping that only uses a small parameter space, which limits the functionality and compactness of the device. Furthermore, the long design cycle required by these techniques reduces design efficiency and technology development. In this paper, we have designed a tunable four-channel wavelength demultiplexer using a recently proposed objective-first algorithm. High performance is achieved for this demultiplexer with a footprint of only 20.16μm2. The peak transmission efficiencies are -1.87 dB, -2.10 dB, -1.68 dB, -1.74 dB and the crosstalk are -14.0 dB, -13.2 dB, -13.7 dB, -16.3 dB at 1453 nm, 1511 nm, 1576 nm, 1639 nm, for each channel, respectively. Moreover, the working wavelength of each channel can be tuned by changing the refractive index of the demultiplexer.

Semitransparent Blue, Green, and Red Organic Solar Cells Using Color Filtering Electrodes

AbstractColorful, semitransparent organic photovoltaic cells (OPVs) are increasing in demand due to their applicability in aesthetically fashioned power‐generating windows. The traditional method of generating different colors in OPVs has been through employing different active materials exhibiting distinct absorption spectra. This can complicate fabrication processes for production and cause deviations in device performance among differently colored OPVs. Herein, semitransparent and colorful OPVs with a single broadband‐absorbing active material of fixed thickness are demonstrated using Ag–TiOx–Ag color filters (CFs). The CF enables the OPV to transmit spectrally pure colors with peak transmission efficiencies surpassing 25%, and allows the colors to be freely tuned without disturbing the charge transport properties such that the device performance stays consistent. The CF not only functions as an effective electrode but as a mirror for light outside of the spectral transparency window. It is shown that when compared to a transparent OPV consisting of the same active layer material and thickness, CF‐integrated OPVs generate 32.38(±0.03)–34.10(±0.02)% more short‐circuit current. Such results point to a simple and convenient solution to achieving spectrally pure colors, moderate transmission efficiencies, decoupled optical and charge transport properties, and enhanced charge generation relative to a transparent OPV in semitransparent, colorful power‐generating windows.

Omnidirectional color filters capitalizing on a nano-resonator of Ag-TiO2-Ag integrated with a phase compensating dielectric overlay.

We present a highly efficient omnidirectional color filter that takes advantage of an Ag-TiO2-Ag nano-resonator integrated with a phase-compensating TiO2 overlay. The dielectric overlay substantially improves the angular sensitivity by appropriately compensating for the phase pertaining to the structure and suppresses unwanted optical reflection so as to elevate the transmission efficiency. The filter is thoroughly designed, and it is analyzed in terms of its reflection, optical admittance, and phase shift, thereby highlighting the origin of the omnidirectional resonance leading to angle-invariant characteristics. The polarization dependence of the filter is explored, specifically with respect to the incident angle, by performing experiments as well as by providing the relevant theoretical explanation. We could succeed in demonstrating the omnidirectional resonance for the incident angles ranging to up to 70°, over which the center wavelength is shifted by below 3.5% and the peak transmission efficiency is slightly degraded from 69%. The proposed filters incorporate a simple multi-layered structure and are expected to be utilized as tri-color pixels for applications that include image sensors and display devices. These devices are expected to allow good scalability, not requiring complex lithographic processes.

Characteristic Analysis of Double Spiral Resonator for Wireless Power Transmission

In this paper, we focused on comprehensive analysis and experiment of a unique resonator pattern, named “double spiral resonator” in wireless power transmission (WPT) via resonance coupling, which is suitable for printing on ultra-thin and low-cost substrates such as paper or film with ink-jet printing technology. By conducting contrast experiments with other two patterns of resonators, the comparing result shows that double spiral resonator ensured higher peak transmission efficiency in longer distance. Five structural parameters of double spiral resonator have been investigated for the effect on the peak transmission efficiency concerned. Also, equivalent circuit (EC) analysis of peak transmission efficiency has also been derived to find the theoretical explanation of the phenomenal parameters' effect on transmission efficiency. We also contributed by exploiting electromagnetic (EM) field calculation method to obtain the coupling coefficient of two double spiral resonators at different distances via the parasitic parameters of the resonators. Lastly, we also conducted a discussion on how parameters can affect the quality factor Q of double spiral resonator.

Color Imaging via Nearest Neighbor Hole Coupling in Plasmonic Color Filters Integrated onto a Complementary Metal-Oxide Semiconductor Image Sensor

State-of-the-art CMOS imagers are composed of very small pixels, so it is critical for plasmonic imaging to understand the optical response of finite-size hole arrays and their coupling efficiency to CMOS image sensor pixels. Here, we demonstrate that the transmission spectra of finite-size hole arrays can be accurately described by only accounting for up to the second nearest-neighbor scattering-absorption interactions of hole pairs, thus making hole arrays appealing for close-packed color filters for imaging applications. Using this model, we find that the peak transmission efficiency of a square-shaped hole array with a triangular lattice reaches ∼90% that of an infinite array at an extent of ∼6 × 6 μm(2), the smallest size array showing near-infinite array transmission properties. Finally, we experimentally validate our findings by investigating the transmission and imaging characteristics of a 360 × 320 pixel plasmonic color filter array composed of 5.6 × 5.6 μm(2) RGB color filters integrated onto a commercial black and white 1/2.8 in. CMOS image sensor, demonstrating full-color high resolution plasmonic imaging. Our results show good color fidelity with a 6-color-averaged color difference metric (ΔE) in the range of 16.6-19.3, after white balancing and color-matrix correcting raw images taken with f-numbers ranging from 1.8 to 16. The integrated peak filter transmission efficiencies are measured to be in the 50% range, with a FWHM of 200 nm for all three RGB filters, in good agreement with the spectral response of isolated unmounted color filters.

Color Filters Based on the Subwavelength Triangular-Lattice Cylinder Arrays in Metal-Dielectric Films

Abstract: Color filter incorporating a subwavelength triangular-lattice cylinder arrays in metal-dielectric films on quartz substrate was proposed. The device consists of a quartz substrate, a triangular-lattice cylinder arrays in both dielectric layer of ZnS and a metallic layer of aluminum (Al). The broadband transmission characteristic of the proposed device in the visible wavelength range was investigated in detail by the rigorous coupled wave analysis (RCWA). Specially by discussing the effects of the structure parameters to the resonant wavelength, typical optimized structure parameters are obtained, in which more than 74.6% peak transmission efficiency with FWHM of ~ 80 nm were simultaneously achieved for the tricolor filters. The simulation results show that the peak transmission efficiency (PET) increases more than 17% with lower color cross-talk compared to the previous color filters.

Highly angle tolerant filter incorporating serially cascaded a-Si based etalons and its application to a compact receiver

A highly angle tolerant spectral filter has been implemented taking advantage of three-stage serially concatenated resonators in dielectric films, each of which involves a high-index cavity in a-Si, sandwiched with a pair of SiO2 films. For the constituent etalons, the free spectral range is individually adjusted by differentiating the thickness of the cavity, so that a primary infrared pass-band could be attained to present enhanced roll-off characteristics in conjunction with an appropriate bandwidth. The a-Si cavities relating to the three etalons are selected to be 117, 234, and 468-nm thick, while the SiO2 layer is uniformly 150-nm thick. The filter is actually created on a silica glass substrate, by alternately depositing SiO2 and a-Si films. The observed center wavelength, bandwidth, and peak transmission efficiency are about 900 nm, 120 nm, and over 90%, respectively, for normal incidence. In response to an angle change amounting to 60°, the relative wavelength shift and the variation in peak transmission become barely 0.03 and 8%, respectively. Finally, a detecting cell is constructed by integrating the prepared filter with a photodiode, thus rendering a 3-dB angular bandwidth of 90°. By adequately arranging three detecting cells in a fixture, a compact, portable optical receiver could then be constructed. For incoming collimated light at λ = 905 nm, the infrared receiver exhibits an extended 3-dB angular acceptance as large as 160°.

Polarization-independent visible wavelength filter incorporating a symmetric metal-dielectric resonant structure

A nanophotonic polarization-independent visible wavelength filter is presented, incorporating a symmetric metal-dielectric resonant structure on quartz substrate, where a sub-wavelength grating, made up of a two-dimensional array of Al square sheets, is integrated with a Si(3)N(4) slab waveguide via an oxide layer. Incident light is orthogonally diffracted by the symmetric grating towards two directions of the grating groove, and then resonantly coupled to both transverse electric and transverse magnetic guided modes associated with the underlying waveguide, irrespective of light polarization. Polarization independent bandpass filtering was thus achieved around specific wavelengths, determined by the grating pitch and the effective index of the waveguide. Three devices, operating in the blue, green and red spectral bands, were built through design and analysis drawing upon the finite-difference time-domain method. The devices, DEV I, II, and III, were constructed with grating pitches of 285, 355 and 395 nm, respectively, while the core was 100 nm thick. They were inspected to function as an efficient bandpass filter, centered at 460, 560 and 610 nm, with bandwidths of about 13, 14 and 17 nm, respectively; the peak transmission efficiencies were consistently over 85%. Furthermore, the transfer characteristics, insensitive to light polarization, were satisfactorily confirmed for normal incidence.

Fiber-to-chip coupler designed using an optical transformation

An integrated silicon photonics coupler for fiber to waveguide conversion was designed employing a transformation optics approach. Quasi-conformal mapping was used to obtain achievable material properties, which were realized by a distorted hexagonal lattice of air holes in silicon. The coupler, measuring only 10 μm in length and fabricated with a single-step lithography process, exhibits a peak simulated transmission efficiency of nearly 100% for in-plane mode conversion and a factor of 5 improvement over butt coupling for fiber to waveguide mode conversion in experimental testing.

Polarizing color filter based on a subwavelength metal–dielectric grating

We propose a polarizing color filter based on a one-dimensional subwavelength metal-dielectric grating combining the functions of a polarizer and a color filter. The proposed device consists of three parts: a substrate, a dielectric grating, and a metal grating. The effects of the dielectric grating and the metal grating are investigated in detail by rigorous coupled-wave analysis. Performance is enhanced effectively by utilizing a dielectric grating of high equivalent refractive index. Typical optimized structural parameters are obtained, in which more than 72.6% broadband transmission with >21 dB polarization extinction ratio are simultaneously achieved for a tricolor filter. For transverse electric (TE) polarized light, its reflection efficiency is more than 71.8% in the broad passband light range, which can be recycled by rotating the TE polarization in part into transverse magnetic polarization and reimpinging on the designed device to increase the total energy efficiency. Numerical results show that peak transmission efficiency (PTE) is increased by at least 12.9% using recycled TE-polarized light.

Color filter based on a two-dimensional submicrometer metal grating

A color filter incorporating a two-dimensional (2D) submicrometer metal grating is proposed. The device is designed by utilizing rigorous coupled-wave analysis (RCWA) and consists of four parts: a polymethyl methacrylate (PMMA) substrate, a dielectric film of high refractive index, a submicrometer grating, and a dielectric overlay of low refractive index. Its performance is enhanced effectively by applying a dielectric film of high refractive index. With a dielectric film height of 30 nm, a grating depth of 70 nm, and an overlay height of zero, three different devices are designed with the following structural parameters: a period of 420 nm for the red, a period of 350 nm for the green, and a period of 260 nm for the blue. For the red filter, the center wavelength is 645 nm and the peak transmission is 72%; for the green one, the center wavelength is 546 nm and the peak transmission is 75%; and for the blue one, the center wavelength is 455 nm and the peak transmission is 71%. The calculated result shows that its peak transmission efficiency increased more than 14% compared to the previous color filters incorporating a grating.

Resonant scattering from two-dimensional gratings

A theoretical investigation of resonant scattering from two-dimensional gratings is presented. Abrupt changes of diffraction efficiency over a small parameter range have been observed by rigorous coupled-wave analysis. The peak reflection or transmission efficiencies can approach unity. This phenomenon is explained in terms of the coupling between the incident plane wave and guided modes that can be supported by the two-dimensional-grating waveguide structure. Because of the double periodicity, the incident field can be coupled into any direction in the grating plane. The guided modes supported by two-dimensional gratings are found by rigorous solution of the homogeneous problem associated with the scattering (inhomogeneous) problem. The complex propagation constants for the guided modes provide estimates of both the resonance angle and width. In addition, to illustrate the implication of the radical change in the phase and amplitude of the propagating waves, we report a study of finite-beam diffraction in the resonant scattering region. Applications for the structures include polarization-independent narrow-band filters and bandwidth-tunable filters. It is shown that, because of the double resonance, the polarization-independent narrow-band filters have a large angular tolerance.